| Noun | 1. | bitterweed - widespread European weed with spiny tongue-shaped leaves and yellow flowers; naturalized in United Statesgenus Picris, Picris - genus of weedy Old World yellow-flowered herbs usually containing a bitter-tasting substance: bitterweed weed - any plant that crowds out cultivated plants |
| 2. | bitterweed - any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthmagenus Ambrosia - comprising the ragweeds; in some classification considered the type genus of a separate family Ambrosiaceae Ambrosia artemisiifolia, common ragweed - annual weed with finely divided foliage and spikes of green flowers; common in North America; introduced elsewhere accidentally Ambrosia trifida, great ragweed - a coarse annual with some leaves deeply and palmately three-cleft or five-cleft Ambrosia psilostachya, perennial ragweed, western ragweed - coarse perennial ragweed with creeping roots of dry barren lands of southwestern United States and Mexico weed - any plant that crowds out cultivated plants |